What I learned while diagnosing the brake actuator

I've been working on my 2007 Camry Hybrid brake error issue for a few days and learned a few things that may help others. I will end up putting in a different unit, but I'm now pretty confident that I've found the issue. The first symptom was the actuator motor running frequently, I assumed this was a leaky accumulator. After some bleeding and resetting, this issue disappeared, but I acquired a C1345 and C1368 (linear valve offset incomplete/failing). It is completely unable to complete the linear valve offset teach. I was able to watch the pressures of the wheel circuits during the valve teach and saw the RL circuit not responding well. I tried some active tests on that circuit (RL: SLARL valve) and found that it was not sealing well: at 0V it would leak pressure and cause the wheel circuit to build pressure. This is likely the cause of the frequent pump running.

I zero'd down the accumulator with the pump relays removed, disconnected that brake line (2nd from the drivers side), loosened the accumulator circuit (empty bleeder valve on block), disconnected the line from the reservoir, and flushed it with brake parts cleaner and compressed air while actuating it's valves in an attempt to clear whatever was preventing sealing. This seamed successful. After reconnecting the lines and flushing that circuit (and accumulator) that circuit sealed up better and would not start building up pressure until about .42 Amps (the other circuits start building pressure around .45 to .5 Amps). The accumulator pressure was also much more behaved, holding pressure for 24 hours, and not even needing to run the next day when I turned the car on. The valve offset still fails, but I got closer.
Running some more tests on the two rear circuits (SLARR and SLARL), I found that the RR side would build pressure in a very square wave with the amplitude dependent on the actuator current. The failing RL side was much more curved, taking longer to get to pressure and going to a much higher pressure. I'm suspecting that the valve is not moving freely enough for the teach routine. Is there much of a possibility that the error is in the coils or wheel cylinder? I've considered getting a brake line plug to eliminate the wheel cylinder from the equation.

 

A few other observations from my troubleshooting:

• All the Front linear valves are normally closed (defaults to the closed position when not powered). As is necessary for the brakes to work in a power failure situation.
• The rear brakes have normally closed SLA linear valves (accumulator or adding pressure), but normally close SLR valves (reservoir or removing pressure). When the brakes are applied or tested, the SLR valves have amperage applied (1.2A during testing of the SLA valves).
• The active test for the SLA valves just give the valves a pulse of current. It doesn't show up on the data screen of techstream and just a blip on the graph. More current = sharper pressure increase and higher pressure.
• The SLA valves do not start acting until about .5 Amps. They open rapidly with .6 Amps. There is likely springs pulling the valves shut (or open for the SLR rear valves) that the coils must act against.
• The linear valve offset appears to be trying to find the current where the pressure can be increased or decreased. If the valve isn't' consistent, the pressure will overshoot/undershoot.

 

Update: I've replaced this brake module with one from a newer salvage car with fewer miles. The system easily performed a air purge and linear valve teach. The valves are much crisper, require slightly more amperage to get them to move (stiffer springs?), and produce a much more square pressure response when tested individually. Also of note: The actuator was still holding pressure when I installed it, the first thing I did was a "zero down" and cycled fluid through the system (opening the SLRFX valves with the system still depressurized and relays still out). Everything works as expected.